About 14 years ago - before I'd taken as much as an intro to CS class - I wrote some software that helped a bar keep track of who'd drank what. They were the type of bar where, if you drank every beer they had available, you'd get a free mug. Prior to it being computerized, the staff used index cards in shoeboxes. Lots of the wait staff's time was lost fumbling through those boxes, unsticking them from each other (gross!), etc.

I've since gotten a degree and written software for a handful of companies.

When I think of how many people are actually _using_ my software, though? Fourteen years later, the mug club software is still live in a production environment, used every day by wait staff who turns over every few months. No doubt hundreds - potentially thousands (it got deployed at a few different bars) - of people have interacted directly with it. That code embarrasses me nowadays, but as far as impact goes: that's probably it.